The present invention relates to storage apparatus for the storage of energy in the form of heat or cold, preferably over a long storage period.
For the supply of the population with power and heat, it is expected that increasing use will be made of solar energy in the future, as direct utilization of solar energy is possible without environmental side effects. For this reason, use of the photo-voltaic solar cell is intensively investigated on a world-wide basis, as it permits sunlight to be directly converted into electricity at an efficiency up to a maximum of 25%.
Electrical current is a high grade form of energy. Amongst other things, current can be used to heat suitable storage masses to high temperatures. If consideration is taken of the fact that half the population of, for example, the Federal Republic of Germany lives in single-family or two-family houses of which the roofs, according to position and orientation, are radiated by solar energy equal to between four and five times the winter heating requirement of such houses, then it would clearly be advantageous to provide for heating of a store to a high temperature with solar cell current and to extract the heat from the store at times when heating is required. As solar energy radiation is at its highest in summer and the greatest requirement for heating occurs in winter, utilization of solar energy necessitates a durable long term heat store which can store the heat supplied in the summer without substantial heat loss before winter and which permits a simple form of heat extraction.
Stores are known for the storage of heat or cold with an external container, an electrically, chemically or thermally heatable or coolable storage mass and an insulating layer arranged between the external container and storage mass. Practice has shown, however, that a heat store of that kind with an insulating layer of natural or synthetic insulating material, for example polyurethane, is not capable of providing adequate insulation over longterm storage periods.
Double-walled liquid gas stores with a granularly porous insulating mass standing under vacuum in an insulating region formed between the double wall are known from a book by Grobner, Erk and Grigull entitled "Grundgesetze der Warmeubertragung" (Springer Verlag, Berlin, Gottingen, Heidelberg) 1963, page 137. However, such stores are intended only for small volumes or else they must be very thick-walled and thus very heavy.
It is accordingly one object of the invention to provide storage apparatus with enhanced thermal insulation so that losses from stored energy in the form of heat or cold are kept to a minimum, particularly over a prolonged storage period.
Another object of the invention is the provision of storage apparatus of uncomplicated and robust construction in which energy can be stored and from which the stored energy can be extracted in a simple manner.
Yet another object of the invention is to provide storage apparatus offering alternative possibilities of energy supply and energy extraction, including inter alia solar-sourced energy.